Method of age hardening magnetostrictive cores



United States Patent 3,084,082 METHOD OF AGE HARDENING MAGNETO- STRICTIVE CORES Pascal Levesque, Needham, and Frederick C. Hawkes, Framingham, Mass, assignors to Raytheon Company, a corporation of Delaware No Drawing. Continuation of application Ser. No. 724,875, Mar. 31, 1958. This application Sept. 29, 1960, Ser. No. 59,158

1 Claim. (Cl. 148-120) This is a continuation of application, Serial No. 724,875, filed March 31, 1958, now abandoned.

This invention relates to magnetostrictive cores and methods for producing them, and, more particularly, to such a core for use as a high Q resonant element in a magnetostrictive filter.

In such filters it is frequently desirable to have a resonant element that will produce a filter of narrow bandwidth and low mechanical loss. Ferro-nickel alloys of the type known as Elin-var have been used for this purpose. By the usual method of preparing such cores it is possible to obtain Qs of only 5,000 when they are used in filters.

By this invention an alloy of this group is specially cold-worked and heat-treated to produce rods for magnetostrictive filters having relatively high electromechanical Qs such as 8,500 and above, as opposed to a Q of 5,000 rods not so worked and treated.

The alloys used are of the following composition by Weight percent:

An ingot of this material is annealed at a temperature of 900 to 1000 Centigrade for a time necessary to bring the minor ingredients of the alloy, such as titanium, carbon and manganese, into solid solution with the nickel and chromium, and is then quenched in water or other suitable quenching agent to room temperature. It is then cold-worked, as by drawing into wire, to reduce the cross section, preferably by more than 90 percent. This severe plastic deformation causes the material to develop high coercive force and low magnetic permeability. After cold-working, the material is raised to a temperature of about 500 C. and held there for between two to three hours, after which it is further heated to a temperature of about 650 C. and held there for an additional period to give a material having a higher mechanical hardness and a temperature coefiicient of Youngs modulus close to zero as a result of precipitation-hardening. For optimum results, the two age-hardening temperatures can be varied somewhat within the limits of 500 C. and 650 C., and the times between two and three hours for different alloy compositions within the range indicated.

A representative core was made according to the method of the invention by swaging a casting of an alloy of the following composition by weight percent:

to A" diameter rod and cold-drawing the rod to 0.149" diameter wire. The Wire was then solution-annealed at 950 C. for half an hour and water quenched, after 3,084,082 Patented Apr. 2, 1963 Nickel 41.5 Chromium 5.5 Titanium 2.5 Carbon Less than 0.04 Manganese 0.3 Iron 50. l 6

A casting of this alloy was cold-drawn to a 0.235" diameter and, after solution-annealing at 950 C. for one-half hour and water quenching, was again cold-drawn to 0.047" diameter Wire, a 96 percent reduction in area, and then heated to 550 C., at which temperature it was held for three hours and then further heated to 625 C., at which temperature it was held for two hours. The resulting core when used in a magnetostrictive filter had a Q of 15,000.

Core wires made according to the process of the invention have high electromechanical Q or low internal friction, moderate magnetostrictive activity, and a temperature coefiicient of Youngs modulus close to zero to produce resonant elements for magnetostrictive filters hav. ing a considerably higher Q with satisfactory operation than cores of the same alloy not so worked and heat treated. The cold working and heat treatment appear to produce a distribution of precipitate which is favorable to the development of the above properties.

This invention is not limited to the particular details of construction, materials, and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claim be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

A method for preparing magnetostrictive material of an alloy consisting of:

Percent by weight in rod form, comprising the steps of solution-annealing the rod at a temperature in the range 900-1,000 C., quenching the rod to a relatively low temperature, coldworking the rod to obtain a reduction in cross-section area of substantially percent or more, and precipitation-hardening the rod successively at a first temperature of approximately 500 C. for a period of substantially three hours and subsequently at a second temperature of approximately 625 C. for a period of substantially two additional hours, thereby to provide a Q of at least 8500.

References Cited in the file of this patent Pilling et al.: Dispersion Hardening Alloys of Nickel and Iron-Nickel-Titanium, paper presented before the Twenty-first Annual Convention of the American Society for Metals, held in Chicago, Oct. 23 to 27, 1939; 31 pages, pages 23-27 particularly relied on.

Eichelberger: Eifect of Aging Cycle on the Properties of an Iron Base Alloy Hardened with Titanium, Transactions American Society for Metals, vol. 50, Preprint No. 21, Sept. 16, 1957; 34 pages, pages 2, 3, 8-13, and 16 particularly relied on. 

